CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

3 The OpenPALM coupler
3.1 Introduction
OpenPALM is a software tool codeveloped by CERFACS and ONERA based on the PALM library (from
CERFACS) and the CWIPI library (from ONERA). OpenPALM is distributed under the open source
license LGPL since the first of January 2011. The distribution is done via a download from the website of
OpenPALM (http ://www.cerfacs.fr/globc/PALM WEB/EN/BECOMEAUSER/download/). After one year
of open access, about 80 downloads have been registred.
This software allows for the concurrent execution and the intercommunication of programs developed
independently one from the other and not having been especially designed for that. In addition to the data
exchange, this coupler offers a number of services, such as intermediate computations on the exchanged
data, grid to grid interpolations, and parallel data redistribution. The couplings therefore span from simple
sequential code assembling (chaining) to complex applications involving tens of components run in parallel
and/or sequentially. Sometimes the components must run in parallel, especially if the coupling exchanges
take place in the inner iterative processes of the computational entities. Furthermore, an important aspect
of OpenPALM is that it allows the components to be launched at any point during the run ; in this sense,
OpenPALM is a dynamic coupler. The main characteristics of OpenPALM are its easy set-up, its flexibility,
its performances, the simple updates and evolutions of the coupled application (one can add a model to the
coupled application without changing the structure of the algorithm) and the many side services it offers.
More generally, the component coupling approach followed by OpenPALM allows for splitting a system
into elementary computational entities that can then be more easily handled and maintained. This approach
has proven to be very effective for the design, the management and the monitoring of large complex systems
as, for instance, data assimilation suites.
The current available version, OpenPALM 4.0.0, implements most of the originally committed functions.
Some tools such as the algebra toolbox (toolbox that interfaces the most common linear algebra
operations) or the opportunity to read/write in NetCDF files have been developed. In addition, some useful
functionalities like the dynamic objects or the possibility to run the units in the driver process have been
implemented. One of the major enhancements of the coupler was to adapt it on new high massively parallel
calculators. Because on this kind of calculators the MPI-2 standard is often imperfectly implemented or
even not implemented at all (IBM Blue Gene), an MPI-1 version of OpenPALM has been developed. Still
in this scope, a brand new communication scheme is being implemented.
In order to provide performant coupling solutions for the aerospace and aeronautic communities either
for the research and industry, CERFACS, ONERA, SAFRAN, EADS and CNES have shared in 2010 an
intensive reflexion on the definition of the next generation coupling tool. A confrontation between existing
tool like Salomé (EDF), CWIPI (ONERA) and PALM (CERFACS) have led to the conclusion that the
existing tools CWIPI and PALM are a very good basis for the development of such an ultimate coupler.
Thus, a collaboration between CERFACS and ONERA is born from this reflexion in order to develop the
open source coupler OpenPALM based on the complementary tools CWIPI and PALM. Current and future
developments of the OpenPALM coupler are based on the tender specifications resulting from the common
104 Jan. 2010 – Dec. 2011